A conventional borehole shear testing device measures soil shearing strength by means of two diametrically opposed shear plates. The shear plates apply a normal stress to the soil forming the wall of the borehole. An axial force is exerted on the shear plates such that the soil shears axially along the borehole. During this conventional test, the normal stress is held constant while the shear head diameter, that is, the distance between the opposing shear plates, is allowed to vary in response to consolidation or dilation of the soil. If the soil consolidates, the head diameter increases. If the soil dilates, the head diameter decreases.
The conventional borehole shear tester imperfectly models the behavior of pile under load. This problem exists because the pile has a constant diameter, and therefore the pile will not yield or compress as the soil consolidates or dilates. Accordingly, in order to simulate pile behavior, the head diameter must be held constant, contrary to the conventional use of the borehole shear tester.
A primary objective of the present invention is the provision of a modified borehole shear tester which simulates pile behavior and which produces a soil normal stress similar to that which develops against a pile surface upon axial loading.
Another objective of the present invention is the provision of an accessory device that can be quickly and easily connected to a conventional borehole shear tester for simulating pile behavior.
A further objective of the present invention is the provision of a method and means for determining soil dilation and consolidation.
Still another objective of the present invention is the provision of a means and method for maintaining a constant shear head diameter while the soil is sheared.
Another objective of the present invention is the provision of a method and means for measuring the normal force and the shearing force as the soil shears, thereby simulating the skin friction on a pile at the moment of failure.